Most of the carbohydrates in plants are in the form of lignocellulose, which essentially consists of cellulose, hemicellulose, and pectin. Cellulose is the major structural component of higher plants. Hemicellulose is a heterogeneous group of carbohydrate polymers containing mainly different glucans, xylans and mannans Pectin consists of a complex set of polysaccharides that are present in most primary cell walls.
Cellulosic material i.e. material comprising cellulose, hemicellulose and/or lignocellulose is degraded in nature by a number of various organisms including bacteria and fungi which produce enzymes capable of hydrolyzing carbohydrate polymers. Degradation usually requires different cellulases acting sequentially or simultaneously. Degradation of more complex cellulose containing substrates requires a broad range of various enzymes.
Lignocellulose can be converted into bioethanol and other chemical products via fermentation following hydrolysis to fermentable sugars. In a conventional lignocellulose-to-ethanol process the lignocellulosic material is first pretreated either chemically or physically to make the cellulose fraction more accessible to hydrolysis. Thereafter the cellulose fraction is hydrolysed to obtain sugars that can be fermented by yeast or other fermentative organisms into ethanol and distilled to obtain pure ethanol. Lignin is obtained as a main co-product that may be used as a solid fuel.
Methods for processing of lignocellulosic biomass have been brought out in U.S. Pat. No. 7,998,713, which discloses a process involving pretreatment of biomass with ammonia. Following pretreatment, the biomass is treated with a saccharification enzyme consortium, i.e. cellulose-hydrolyzing glycosidases, to produce fermentable sugars. The sugars are then contacted with a microorganism that can ferment the sugars and produce ethanol. US20080032344 discloses a process for treating biomass to separately recover holocellulose and near-native lignin therefrom whereby the lignin and holocellulose-derived sugars can then be subjected to different treatments to produce fuels, chemicals, and/or new materials.
Processing of biomass by lignocellulolytic enzymes has significant potential applications in biofuel, starch, textile, detergent, pulp and paper, food, feed or beverage industry. In many of these applications xylanases are used in connection with various other lignocellulolytic enzymes. In paper and pulp industry xylanases are used in papermaking to reduce chlorine consumption and toxic discharge during bleaching of wood pulp, in textile processing to reduce or replace chemical retting, in bioremediation/bioconversion to treat/recycle wastes and to produce biofuels and fine chemicals and in baking to improve the elasticity and stability of dough or the volume and anti-staling properties of the baked product. WO2011091260 discloses compositions and methods for treating lignocellulosic material with a dual activity enzyme having xylanase and cellulase activity. The enzyme is stable and active at increased pH and increased temperatures. US20120036599 discloses novel fungal enzymes isolated from Chrysosporium lucknowense C1 (now reindentified as Myceliophthora thermophile; Visser et al., 2011) suitable for biomass processes, detergent processes, deinking and biobleaching of pulp and paper and treatment of waste streams.
Enzymes degrading hemicellulose, such as hemicellulases, xylanases, pectinases and esterases have been used to improve the break-down of plant cell walls e.g. in animal feed compositions. Especially ferulic acid esterases have been observed to act synergistically with xylanase to release ferulic acid from plant cell walls. CN101228921 discloses a composition of ferulic acid esterase, cellulase, xylanase and dextranase for feed stuff, which enzymatically improves release of sugar from animal feed. U.S. Pat. No. 6,143,543 discloses an enzyme obtainable from Aspergillus and having ferulic acid esterase activity, which is useful for preparing food and animal feed. Polypeptides from Humicola insolens having feroyl esterase activity are disclosed in US20090151026. Kühnel et al. 2012 disclose ferulic acid esterases of Chrysosporium lucknowense C1, which are most active at neutral pH and temperatures up to 45° C.
The cost and hydrolytic efficiency of the enzymes are the major factors that restrict the extensive use of biological hydrolysis processes for biomass conversion. The hydrolytic efficiency of enzyme complexes in the process of lignocellulose saccharification depends both on properties of the individual enzymes and the ratio of each enzyme within the complex. In addition to improving characteristics with respect to individual enzymes in the enzyme complex it is beneficial to improve the enzymatic degradation of cellulosic material by influencing on the activity of cellulases. Furthermore, optimization of the components in enzyme complexes and supplementation of synergistically acting enzymes are needed to improve hydrolytic efficiency.
Hence, there is still a continuous need for new efficient methods of degrading cellulosic substrates, in particular lignocellulosic substrates, and for inexpensive enzymes and enzyme mixtures, which can considerably improve the enzymatic degradation of cellulosic material and also reduce the required enzyme dosage. Moreover, there is a need for processes which work not only at moderate temperatures but also at high temperatures, thus increasing the reaction rates and enabling the use of high biomass consistency leading to high sugar and ethanol concentrations. Because of environmental concerns and consumer demands, alternative enzyme-aided technologies have been desired. Furthermore, there is a need for enzymes and processes, which can be used in a variety of agricultural and industrial applications and which allow the design of more flexible process configurations.
The present invention aims to meet at least part of these needs.